This application claims the benefit of Japanese Patent Application P2002-100,130, filed on Apr. 2, 2002, the entirety of which is incorporated by reference.
1. Field of the Invention
The invention relates to a device for generating blue laser beam having a wavelength of 457 nm with a high efficiency.
2. Related Art Statement
In the field of optical information processing, it has been demanded a blue laser oscillator capable of oscillating blue laser beam having a wavelength of about 400 to 430 nm at a power of not lower than 80 mW for realizing high density optical recording. Suppliers have been competed for supplying such device in a market. As such a light source for generating blue laser beam, it has been expected an optical waveguide-type device for converting wavelength having a laser beam source oscillating red light as fundamental wave and a second order harmonic wave generator of quasi-phase matching system.
In particular, blue laser beam having a wavelength of about 457 nm has been strongly demanded for various applications including blue light source of RGB (three primary colors) system, print laboratory, projector or the like. An output of not lower than 200 mW has been demanded depending on the application.
Japanese patent publication 293,268A discloses a system for oscillating blue laser beam having a wavelength of 460 nm. In the system, Nd-YAG laser beam with a wavelength of 1064 nm is used for oscillating second harmonic wave with a wavelength of 532 nm. Infrared light of 3.3 micrometer is oscillated by means of parametric oscillation of the light with a wavelength of 1064 nm. The light of 460 nm is oscillated as sum frequency of the light of 532 nm and infrared light of 3.3 micrometer. This system needs three devices each for converting wavelength The total conversion rate is low and unpractical.
Japanese patent number 3,260,457 discloses a system for oscillating blue laser beam. In the system, excitation light having a wavelength of 809 nm is irradiated onto Nd-doped YAG crystal to oscillate laser beam having a wavelength of 946 nm. The laser beam of 946 nm is then irradiated to a second harmonic wave generator provided in an MgOxe2x80x94LN substrate installed in a resonator so that the wavelength of the laser beam is converted to 473 nm. 10 mW of the laser beam with a wavelength of 473 nm is obtained when an output of the laser beam of 946 nm is 200 mW so that a total efficiency of light-light conversion is 5 percent.
According to Japanese patent publication 6-194,706A, a semiconductor laser device outputs laser beam having a wavelength of 880 nm. The laser beam is irradiated onto a second harmonic wave generator of proton exchange optical waveguide type formed in an MgOxe2x80x94LN substrate to obtain laser beam of a wavelength of 440 nm. A power of 12 mW is attained when the power of the semiconductor laser is 100 mW.
In Japanese patent publications 5-11289A and 5-90687A, it is briefly described that a laser device may be fabricated using Nd:YVO4 and KNbO3 for oscillating laser having a wavelength of 457 nm. No experimental evidence is presented.
Similar description is found in Japanese patent publication 5-248659A. Moreover, it is briefly described that sum frequency of semiconductor laser beam having a wavelength of 809 nm and Nd:YVO4 laser beam having a wavelength of 1064 nm is generated using KTP crystal. No numerical description is found.
Japanese patent publication 9-502054A disclosed laser device generating laser having a wavelength of 457 nm or 456 nm. This device utilizes Nd:YVO4 or Nd:GdVO4 crystal and KNbO3 or BBO crystal for generating second harmonic wave. This device is a kind of internal resonator type having a wavelength converting device installed in a resonator for laser oscillation, and its structure is thus substantially different from that of the present invention. The output and efficiency are not described.
As described above, it has not been presented an example successfully oscillating blue laser beam having a wavelength of about 457 nm at a high efficiency and power.
Laser oscillation based on 4F3/2-4I9/2 transition of Nd doped YVO4 crystal is described in (OPTICS LETTERS) Vol. 25, No. 01, (2000) January, pages 34 to 36. That is, excitation light having a wavelength of 808 nm is irradiated onto Nd-doped YVO4 crystal to oscillate laser beam having a wavelength of about 914 nm.
The inventors have studied to utilize such laser beam having a wavelength of about 914 nm to oscillate second harmonic wave, that is, blue light having a wavelength of 457 nm. The threshold for oscillation of laser beam having a wavelength of 914 nm is as high as about 3.5 W according to the publication. The slope efficiency is low and heat generation is considerable. It is thus difficult to obtain a device for oscillating blue light beam with a low driving voltage due to the high threshold of laser oscillation. It is also difficult to obtain a practical device for oscillating blue light due to the low slope efficiency and generation of a large heat.
An object of the present invention is to provide a practical device for oscillating blue laser beam having a wavelength of about 457 nm.
The present invention provides a device for oscillating blue laser beam having a solid laser oscillator composed of Nd-doped YVO4 crystal and having a length of not smaller than 0.1 mm and not larger than 1.0 mm, a reflecting means provided in the solid laser oscillator, an illuminating means for illuminating excitation light beam to the solid laser oscillator, and a waveguide-type device for generating harmonic wave. The solid laser oscillator and reflecting means constitute a resonator. The waveguide-type device is provided outside of the resonator. The solid laser oscillator oscillates laser beam having a wavelength of 914xc2x11 nm and the waveguide-type device oscillates blue laser having a wavelength of 457xc2x11 nm.
The present invention further provides a method of oscillating blue laser beam, using a solid laser oscillator composed of Nd-doped YVO4 crystal and having a length of not smaller than 0.1 mm and not larger than 1.0 mm, a reflecting means provided in the solid laser oscillator, and a waveguide-type device for generating harmonic wave. The solid laser oscillator and the reflecting means constitute a resonator. The waveguide-type device is provided outside of the resonator. The excitation light beam is irradiated to the solid laser oscillator so that the oscillator oscillates laser beam having a wavelength of 914xc2x11 nm and the waveguide type device oscillates blue laser having a wavelength of 457xc2x11 nm.
The inventors have successfully provided a device for oscillating blue laser beam having a wavelength of 457xc2x11 nm by means of the structure described above and thus successfully provided a practical device for oscillating blue laser beam.
The blue laser beam having a wavelength of 457 nm is suitable for a blue light source for use in RGB (three primary colors) system. A blue light source having a low oscillation threshold and heat generation has been strongly demanded. The present invention provides a substantial progress in this field.
The present invention will be further described below. FIG. 1 is a view schematically showing major states in Nd-doped YVO4 crystal. When excitation light beam of 808 nm is irradiated onto and absorbed into Nd-doped YVO4 crystal, electrons in the crystal are excited from ground state to 4F5/2 state. After the excited electrons are then relaxed from 4F5/2 state shown as xe2x80x9cPxe2x80x9d, transition of the electrons occur from 4F3/2 state to 4I11/2 or 4I9/2 state. Photons are generated during the transition. Light having a wavelength of 914 nm is oscillated based on the transition of 4F3/2 to 4I9/2 states, and light having a wavelength of 1064 am is oscillated based on the transition from 4F3/2 to 4I11/2 states.
According to ┌OPTICS LETTERS┘ Vol. 25, No. 01, (2000) January, pages 34 to 36, excitation light with a wavelength of 808 nm is irradiated onto Nd-doped YVO4 crystal to oscillate light with a wavelength of 914 nm.
The inventors have tried to illuminate excitation light with a wavelength of 880xc2x12 nm onto a laser oscillator composed of Nd-doped YVO4 crystal to excite electrons directly to 4F3/2 state. The subsequent transition of the excited electrons to 4I9/2 state results in oscillation of light with a wavelength of 914 nm. It is thus possible to reduce a threshold value of the oscillation of light with a wavelength of 914 nm and to improve the slope efficiency.
According to ┌APPLIED PHYSICS LETTERS┘ Vol. 79, No. 5, (2001) July, pages 590 to 592, light with a wavelength of 885 nm is irradiated onto Nd-doped YAG ceramics to excite electrons. The transition of the excited electrons from 4F3/2 state to 4I11/2 state results in oscillation of laser beam with a wavelength of 1064 nm. It is not, however, described oscillation of laser beam resulting from the transition of electrons from 4F3/2 state to 4I9/2 state.
The effects, features and advantages of the invention will be appreciated upon reading the following description of the invention when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art.